Human interface design for semi-autonomous control of leader-follower excavator based on variable admittance and stagnation/trajectory bifurcation of nonlinear dynamics

Abstract

Conventional remote operation of an excavator has low work efficiency comparing with on-site operations. This is because it is difficult for an operator to recognize the excavator status and surrounding environments. Moreover, there are restrictions such as a limitation on the amount of information that can be transmitted, delays in communication, and harsh environments that cause sensor failure. Therefore, we have developed a semi-autonomous control system that consists of autonomy and human manipulation. This paper proposes (1) a bilateral control system based on variable admittance and (2) an autonomous control using nonlinear dynamics that has attractors with stagnation and trajectory-bifurcation. (1) In the proposed method, the admittance parameters are changed based on the difference between the leader and follower position. We implement the proposed method into a prototype of excavator and verify the operation with two types of external environmental forces: free movement and contact with a rock. (2) The attractor's stagnation is designed as a sink of vector field converging to an arbitrary point on the trajectory. A stagnation is placed at a trajectory's bifurcation point, and the operator selects the next operation by adding a force to the leader system, which is measured through a force sensor. We design two types of bifurcating attractors and conduct an experimental verification of the proposed semi-autonomous control system.

Discrete / continuous task bifurcation by frequency separation of human operation for semi–autonomous excavation

“…In the context of pHRI (Physical Human-Robot Interaction), Khoramshahi et al (2018) have proposed transforming the task trajectory using a cooperative robot to adapt a parameterized dynamic system to the human intended task online. However, no method has been proposed to combine task selection (as proposed in (Okada et al, 2021;Pistillo et al,2011;Khoramshahi et al, 2019)) and task trajectory deformation (as proposed in (Okada et al, 2020;Khoramshahi et al, 2018)) in nonlinear dynamics in a single robot to achieve operation separation. We contribute to these research areas by proposing a semi-autonomous leader-follower system that deforms the task trajectory in a nonlinear dynamical system with attractor and achieves operational separation between task selection and trajectory deformation.…”

“…x = θ x y ϕ T is the state variable of each robot, θ is the turning angle, x and y are the position of the base of the bucket, ϕ is the absolute angle of the bucket, and the subscripts l and f represent leader and follower. This system is based on methods described in our previous paper (Okada et al, 2021), with the addition of the trajectory deformation elements described in Section 4. Full details of the methods used can be found in this previous paper.…”

“…However, Yamauchi et al (2019) have reported that the conventional method using LCD monitors (displaying side, front, and cockpit views) and a joystick for operation reduces work efficiency to less than 50% compared to direct operation. To address this issue, our previous work has introduced a semi-autonomous system that combined autonomy and human intervention (Okada et al, 2021). This approach provides a leader-follower system with a same structured leader system as the follower (hydraulic excavator) and an attractor-based controller, effectively addressing several challenges related to force transmission and discrete task selection shown in Fig.…”

Another Mechanism for Gait Generation: Mechanical Stabilization Can Spontaneously Realize Walking in a Two-Legged Robot

“…Aoi et al demonstrated the advanced turning maneuvers of a multilegged centipede robot using the bifurcation phenomenon as a parameter of the flexibility of its body segments [40]. In a study of bifurcated gait transitions, a semi-autonomous control system with two bifurcated attractors was proposed [41]. This robot motion transition exhibits an example of successfully using the stabilization and destabilization of a nonlinear dynamical system and is expected to realize highly efficient motion control because the system as a whole actively moves toward a stable state (attraction phenomenon).…”

Framework to Estimate Operating Intention for a Leader–Follower Robot

“…Many studies on leader-follower robots aim at achieving "human-machine integration" control [6][7][8][9][10][11][12][13][14]. This approach emphasizes mirroring human motion in robot actions, which enables precise control.…”